From a bubble chamber exposure in an antiproton beam at 5.7 GeV/ c yielding 13 events/μb, the final states p ̄ p → Y 1 ∗+ (1385)Λ, Y 1 ∗+ (1385)Σ + , Y 1 ∗+ (1385) Y 1 ∗+ (1385) have been isolated. We have measured the total cross section, d σ /d t , and the complete density matrix of the Y ∗ for these processes. Upper limits have been set to the forbidden reactions p ̄ p → Y 1 ∗− (1385)Σ − , Y 1 ∗− (1385) Y 1 ∗− (1385) .
No description provided.
We report experimental results on the cross section for the reaction e + e − → hadrons as a function of the total c.m. energy in the range W = 1.42–3.09 GeV. The results, combined with those already existing below the charm threshold, clearly indicate a structure for R ( W ) = α ( e + e − → hadrons)/ α ( e + e − → μ + μ − ) in that energy region.
THE ENERGY RANGES OF THE NEW DATA AND THE PREVIOUS (REVISED) DATA OVERLAP BETWEEN 1.9 AND 2.0 GEV. RADIATIVE CORRECTIONS HAVE BEEN APPLIED TO ALL DATA. THIS CROSS SECTION EXCLUDES TWO-BODY FINAL STATES.
The quasifree p+n→d+η reaction cross section has been measured at the threshold using 1295 MeV protons in the CELSIUS storage ring and an internal cluster-jet deuterium target. The kinematics is chosen such that the target proton can be assumed to be a spectator. The Fermi momentum of the target neutron is used to extract the energy dependence of the cross section by reconstructing the kinematics on an event-by-event basis. The data cover excess energies from threshold to 10 MeV in the center of mass of the final dη system. Approaching the threshold the cross section is enhanced compared to what is expected from phase space. This behavior is typical for a strong final-state interaction.
Cross section as a function of the C.M. excess energy.
Three-jet production is studied for the first time in deep-inelastic positron-proton scattering. The measurement carried out with the H1 detector at HERA covers a large range of four-momentum transfer squared 5 < Q^2 < 5000 GeV^2 and invariant three-jet masses 25 < M_(3jet) < 140 GeV. Jets are defined by the inclusive k_T algorithm in the Breit frame. The size of the three-jet cross section and the ratio of the three-jet to the dijet cross section R_(3/2) are described over the whole phase space by the predictions of perturbative QCD in next-to-leading order. The shapes of angular jet distributions deviate significantly from a uniform population of the available phase space but are well described by the QCD calculation.
Distribution of jet energy fraction X3 = 2E(P=4)/M(P=4_5_6) in the 3 JET centre-of-mass frame for Q**2 from 5 to 100 GeV**2.
Distribution of jet energy fraction X3 = 2E(P=4)/M(P=4_5_6) in the 3 JET centre-of-mass frame for Q**2 from 150 to 5000 GeV**2.
Distribution of jet energy fraction X4 = 2E(P=5)/M(P=4_5_6) in the 3 JET centre-of-mass frame for Q**2 from 5 to 100 GeV**2.
Cross-section and angular distributions for hadronic and lepton-pair final states in e+e- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant alphaem at LEP2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the gamma-Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.
CM energy values.
An analysis of the three leptonic reactionse+e−→e+e−,μ+μ− andτ+τ− over a wide range of energy,\(12< \sqrt s< 46.78 GeV\) is presented. The data were obtained with the JADE detector at thee+e− storage ring PETRA. They are compared to predictions of electroweak theories, in particular the standard model. For the total cross-sections of all three reactions and for the differential cross-section of Bhabha scattering no deviation from QED is found over the entire energy range. The differential cross-sections of μ and τ pairs at high energies show the angular asymmetry predicted by electroweak interference. The axial-vector and vector weak coupling constant, sin2θW andMZ are determined and compared to other measurements. Finally, limits on deviations from the standard model are given.
No description provided.
The production and decay of τ-pairs was studied with the JADE detector at PETRA at center-of-mass energies of 30 ⩽√ s ⩽ 46.78 GeV. The total production cross section for τ-pairs agreed with QED predictions to order α 3 . Lower limits on QED cut-off parameters of Λ + > 285 GeV and Λ − > 210 GeV at 95% confidence level were ontained. The decay branching fractions into one and three charged particles were determined to be (86.1 ± 0.5 ± 0.9)% and (13.6±0.5 ±0.80)%. In the angular distributions a forward-backward asymmetry was observed, from which the axial-vector weak charge to the τ was determined to be a τ = −0.74 ± 0.22 in agreement with the standard model. An analysis of the process e + e − → τ + τ − γ showed agreement with QED calculations to O(α 3 ).
Includes data from earlier analysis at lower energy - M. Nozaki - Tokyo - UTLICEPP-82-02.
None
No description provided.
The process e^+e^- --> Z gamma, where the Z boson decays into hadrons or neutrinos, is studied with data collected with the L3 detector at LEP at centre-of-mass energies from 189 GeV up to 209 GeV. The cross sections are measured and found to be in agreement with the Standard Model predictions. Limits on triple neutral-gauge-boson couplings, forbidden in the Standard Model at tree level, are derived. Limits on the energy scales at which the anomalous couplings could be manifest are set. They range from 0.3 TeV to 2.3 TeV depending on the new physics effect under consideration.
Cross sections as a function of c.m. energy.
Deep inelastic scattering and its diffractive component, ep -> e'gamma*p ->e'XN, have been studied at HERA with the ZEUS detector using an integrated luminosity of 4.2 pb-1. The measurement covers a wide range in the gamma*p c.m. energy W (37 - 245 GeV), photon virtuality Q2 (2.2 - 80 GeV2) and mass Mx. The diffractive cross section for Mx > 2 GeV rises strongly with W: the rise is steeper with increasing Q2. The latter observation excludes the description of diffractive deep inelastic scattering in terms of the exchange of a single Pomeron. The ratio of diffractive to total cross section is constant as a function of W, in contradiction to the expectation of Regge phenomenology combined with a naive extension of the optical theorem to gamma*p scattering. Above Mx of 8 GeV, the ratio is flat with Q2, indicating a leading-twist behaviour of the diffractive cross section. The data are also presented in terms of the diffractive structure function, F2D(3)(beta,xpom,Q2), of the proton. For fixed beta, the Q2 dependence of xpom F2D(3) changes with xpom in violation of Regge factorisation. For fixed xpom, xpom F2D(3) rises as beta -> 0, the rise accelerating with increasing Q2. These positive scaling violations suggest substantial contributions of perturbative effects in the diffractive DIS cross section.
Cross section for the diffractive scattering process GAMMA* P --> DD X for a diffractive mass of 3.0 GeV and Q**2 = 2.7 GeV**2.
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